Typically during the manufacturing of coating compositions, such as automotive OEM or refinish paints, from time to time, an aliquot of such coating compositions being manufactured is taken, applied as a layer of desired thickness over a test substrate, dried and/or cured into a coating and it's gloss measured. The process parameters are then adjusted and the aforedescribed testing procedure is repeated until the adjusted coating composition meets the gloss requirements.
The aforementioned testing procedure is not only time consuming and cumbersome but it also results in frequent interruptions in the manufacturing process. As a result, the batch-to-batch quality of the resulting coating compositions can be affected detrimentally. Several methods have been developed to measure optical properties of a layer from a coating composition in its wet state that correlate to the gloss that can result when such a layer dries and/or cures into a coating. However, since the optically proprieties of a wet layer of a coating composition continuously changes due to evaporation of solvent from and/or crosslinking of the wet layer, it becomes difficult to correlate such wet optical property measurements to the gloss of a coating that results from such a layer once it dries and/or cures into a coating. To get around the aforementioned problem, the color properties of a liquid composition stored in a clear glass container could be measured. However, such a solution still does not provide an accurate correlation to what the gloss of the resultant coating would be due to distortions introduced by the reflection and refraction of light beam passing through the walls of the clear glass container. To address the aforedescribed problems, the commonly assigned U.S. Pat. No. 6,292,264 provides for a circulating carrier strip over which a layer of coating composition is applied and then its optical properties are measured by a non-contact optical device soon after the layer is cast over the carrier strip as it passes underneath the optical device. However, the need still exists to develop a process that correlates the optical properties of a wet layer of a low gloss coating composition containing flatting agent to predicting the gloss of the coating resulting from such a layer.